Typical peak flow factors range from 4 to 6 for smallareas down to 1.5 to 2.5 for larger areas. An allowancefor unavoidable infiltration of surface and subsurfacewater into the lines is sometimes added to the peak flowto obtain the design flow. A typical infiltration allowanceis 500 gallons per inch of pipe diameter per mile ofsewer per day. From the types of sewage and theestimated design flow, the engineer can then tentative] yselect the types, sizes, slopes, and distances below gradeof the piping to be used for the system.Then preliminary drawings of the system areprepared. The preliminary drawings should include bothplans and profiles of the proposed wastewater systemand all buildings, roads, waterways, utilities, geology,and so forth, that may affect the design. As an EA, youmay be called upon to assist in the preparation of thepreliminary plans. When existing topographic maps ofsufficient detail are available, they may be used inselecting the routing of the proposed system. However,when existing maps are not available or to ensuresufficient detail, you may be required to conducttopographic and preliminary route surveying uponwhich the routing will be based. The procedures forthese surveys are explained in chapters 8 through 10 ofthis manual.Upon acceptance of the preliminary designs, finaldesign may begin. During this phase, adjustments to thepreliminary design should be made as necessary, basedupon additional surveys, soil analysis, or other designfactors. The final designs should include a general mapof the area that shows the locations of all sewer lines andstructures. They also should include detailed plans andprofiles of the sewers showing ground elevations, pipesizes and slopes, and the locations of any appurtenancesand structures, such as manholes and lift stations.Construction plans and details are also included forthose appurtenances and structures.Q1.Q2.Q3.Q4.Q5.Q6.Q7.Q8.Q9.Q1O.QUESTIONSName the two systems that comprise an overallpower system.What system of arranging primary feeders is theleast reliable but the most commonly used?What is the purpose of a distribution trans-former?In relation to the primary mains, where on apower distribution pole should the secondarisbe located?Under what circumstances are concrete powerdistribution poles authorized for use on a Navyinstallation?On a drawing of an overhead electrical dis-tribution system what information should youshow for the overhead conductors?Define water table.What three primary factors must an engineerconsider when selecting a water source?When, if ever, is it permissible to install a waterline and a sanitary sewer line in the same trench?In a waste water system, what is the purpose of alift station?2-22